This section introduces aspects that may be helpful to facilitating a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
The rapid growth of Internet and cloud computing applications drives an increasingly significant demand for capacity of communication networks. With the commercialization and deployment of 100 Gb/s technologies using polarization-division-multiplexed quadrature-phase-shift-keying (PDM-QPSK) and digital coherent detection in optical transport networks, and the development of higher bit rates such as 400 Gb/s and 1-Tb/s technologies, there is also an urgent need to upgrade metro networks from 10 Gb/s to 100 Gb/s or greater in the near future. Digital coherent detection is one way to achieve high spectral efficiencies and networking flexibilities. However, compared with optical transport networks, metro networks are more sensitive to cost, footprint, and power consumption. There is a significant need for low-cost optical transmission systems that meet the future requirements of metro networks.